The present invention relates to what has been claimed in the preamble and thus refers to the field of energy storage means.
In order to be able to give good supply of electrical energy to mobile electrical devices, machines and vehicles, high-performance energy storage means are required. The demands on such energy storage means are growing with the desire to be able to open up new applications or to be able to provide higher-performance equipment, for example for electrical/hybrid vehicles. Energy storage means are typically rechargeable batteries, which are also referred to as accumulators or as secondary cells.
In principle, batteries consist of two different electrodes, between which there is an electrolyte. In the case of lithium ion batteries, for example, one electrode, namely the negative electrode, is formed from graphite, while the positive electrode may be formed from lithium metal oxide. In general, it is desirable to be able to draw large currents from an energy storage means over a prolonged period. In order to ensure this, the electrodes are made thin and are arranged closed to one another. Between the electrodes, specifically in the case of particularly compact batteries with low electrode separation, there is an electrically insulating separator permeable to the ions of the electrolyte, which prevents internal short circuits.
In order to be able to form a thin electrode, it is already known that the electrode starting material can be provided in powder form and the electrode can be produced from this starting material by means of film casting. Film casting is a primary shaping process for production of thin, large-area ceramic films, in which the ceramic powder—here the lithium-containing ceramic powder—is processed with the aid of suitable substances and additives to give a free-flowing casting slip. In a film casting system, this ceramic slip can be applied, for example, to a continuous metal foil and smoothed continuously under a coating bar. The slip layer thus obtained can be dried and processed further.
An advantage of such electrodes is the high porosity, which leads, after filling with an electrolyte, to low maximum diffusion pathways of the charge carriers from the electrode material into the electrolyte, and hence rapid charging and discharging of the battery.
There have already been proposals to use thin electrode layers, for example layers having thicknesses below 5 μm, as producible by HF magnetron sputtering, for improvement of the electrochemical properties of a battery in which corresponding electrodes are used, by means of short UV laser pulses. This introduces additional conical pores into the material. The improvement achieved in the electrochemical battery properties through such compact thin layers is attributed to the fact that the diffusion pathways of the lithium ions through the material toward the electrolyte are shortened because of the laser structuring, which is said to enable more rapid charging or discharging of the battery cell.
The literature also describes the increase in the surface areas of thin-film electrodes for improvement of the battery properties using the term “three-dimensional battery”. In this context, there have already been studies of prestructuring of the substrate and the subsequent deposition of electrodes on the substrate structures obtained. Reference should be made, for example, to the review article “Three-dimensional Battery Architectures” by J. W. LONG et al., Chem. Ref. 2004, 104, 4463-4492.
With regard to the known techniques mentioned, reference should be made firstly to the article “Laser annealing of textured thin film cathode material for lithium ion batteries” by R. KOHLER et al., Laser-based Micro- and Nano-Packaging and Assembly IV, Proceedings of SPIE, Volume 7585, p. 758500-11. Reference should also be made to the article “Laser-assisted structuring and modification of LiCoO2 thin films” by R. KOHLER et al., Proceedings of the SPIE (2009), Volume 7202, p. 720207-720207-11, and to the article “Patterning and annealing of nano-crystalline LiCoO2 thin films” by R. KOHLER et al., Journal of Optoelectronics and Advanced Materials, Volume 12, No. 3, March 2010, pages 547-552.
As regards films for electrochemical components and processes for production thereof, reference should be made, merely by way of example, to EP 1 230 708 B1.
Reference should also be made to DE 699 27 556 T2 and the articles “High Energy Density All-Solid-State Batteries: A Challenging Concept towards 3D Integration” by LOIC BAGGETTO et al., Advanced Functional Materials 18 (2008), 1057-1066, and to the article “Nanomaterials for rechargeable lithium batteries” by P. G. BRUCE et al., Angewandte Chemie-International Edition, 2008, 47(16), p. 2930-2946, and the article “3D Micro Batteries” by R. W. HART et al., Electrochemistry Communications 5 (2003), p. 120-123.
A specific problem in the case of high-performance energy storage means arises in the production of the cell. In this context, it has to be ensured that the electrolyte is distributed homogeneously between the electrodes. If this is not assured, meaning that the electrolyte is distributed inhomogeneously during the cell assembly, the areas of the electrode not wetted by the electrolyte cannot be utilized for the storage of electrical charge; the cell does not reach the specified capacity and can fail prematurely. The achievement of a homogeneous electrolyte distribution during the cell production is thus a quality-determining process step. For this reason, the filling of the cell, according to the prior art, is performed in a process which envisages multiple filling with alternate production of a vacuum in the space between the cell package and the electrode stack and subsequent aging for several hours. This operation is exceptionally time-consuming and is associated with various manual operating steps and therefore costly.
It is desirable to be able to improve the properties of a battery, especially when large-area elements with low spacing which come into contact with electrolyte are to be introduced into the battery. More particularly, but not exclusively, it is desirable to improve properties of electrodes formed from pulverulent material and/or with a thickness of the active material of more than 10 μm.
US 2005/0053833 A1 discloses a nonaqueous electrolyte battery, the electrode arrangement of which has a high-density positive electrode in which the positive electrode material is formed on at least one surface of the positive electrode current collector, and in which a separator interposed between the positive and negative electrodes is provided, and in which a structure in which the electrode arrangement is formed with a nonaqueous electrolyte is formed, wherein the specific surface area per unit area of the layer of active material of the active material layer of the positive electrode is 0.5 to 1.0 times the specific surface area per unit area of the active material layer of the negative electrode which opposes the positive electrode with the separator therebetween.
DE 103 43 535 C5 discloses a separator for lithium-polymer batteries with a profiled surface, wherein the separator is 10 to 40 μm thick and the profiled surface has a profile depth of 3 to 5 μm.
DE 10 2006 035 468 A1 discloses provision of modified electrodes for electrical energy storage means, more particularly for lithium ion batteries, having a structured surface. In this case, the intention is to structure a cathode electrode, this structuring being effected simultaneously in the course of production in a laminator. Capillaries are produced. In the course of filling of the cells, these capillaries are supposed to conduct the electrolyte, as a result of their capillary action, onward into the middle of the wound cathode electrodes, i.e. into the middle of the cell. This enables filling of the lithium ion cells in a single step.
It is an object of the present invention to provide something novel for commercial use. Preferred embodiments can be found in the dependent claims.